Meetup group: League of Extraordinary Algorithms -- Special Topic: Molecular Manufacturing (past - was on 2018-05-12) -- link]]>Paper title:
"On the effect of local barrier height in scanning tunneling microscopy:
Measurement methods and control implications"
doi.org/10.1063/1.5003851I'll try to summarize in a reader friendly way.
(I found abstract and conclusion of this paper…]]>Sun, 18 Feb 2018 14:18:49 +0000Paper title:
"On the effect of local barrier height in scanning tunneling microscopy:
Measurement methods and control implications"doi.org/10.1063/1.5003851

I'll try to summarize in a reader friendly way.
(I found abstract and conclusion of this paper not really satisfying.)

One of the most serious issues with current STM microscopes
is their tendency to fail on some more severe surface features like e.g.
chemically highly reactive sites including dangling bonds.

(Since I've once worked with an STM (omicron) I know that pain all too well.
Exactly where it gets interesting one gets all those "shadows" where the feedback control fails.)

So from the squared slope of the logaritmized tunneling current one can determine the work function average. Since this value is position dependent one can obtain a local-work-functon-image better known as local-barriere-height (LBH) image.

Now here's the problem:

Reversely, varying the current always in the same way, meaning independent of the LBH at the current position, produces different variation amplitudes of delta depending on the local work function. What most current (2018) STMs are using is PI control that uses exactly that position independent constant gain. And this is what regularly gets them into an unstable regime (a regime where the actual current widely detours from desired current) at locations with low LBH. This is leading to the aforementioned "shadows".

Here's what the papers authors did to solve the issue:

They superimposed a "high" frequency dithering signal (dither frequency was 4kHz) onto the unprocessed feedback signal such that they could determine the LBH based on the resulting current variations. (This part was not new.)

Then they use the gained LBH value to continuously (LBH estimation bandwidth was 400Hz)
re-tune the DC gain of the STM's PI controller. Re-tune the the proportional P part. (PI Feedback bandwidth was 300Hz.)

As a side-note: They used some alternative implementation of a lock in amplifier including second order band pass filters and first order Lyapunov filters. They write that they have outlined details about that in one of their preceding papers.

The results:

(Fig. 5.):
(1) Significant reduction of the unwanted correlation of the LBH images with the topography images.

(Fig. 6):
(2) At the usually wanted and or necessary high gain settings near the stability limit, sudden drops in LBH (like in case of dangling bonds) do no longer lead to PI control breakdown. The old "solution" of reducing the overall gain led to more tip-sample crashes (especially in lithography mode) due to less sensitivity and smaller bandwidth.

(Note: The shadows are no crashes. They are more like over-retracts. When lowering DC gain to reduce these shadows, this is when one gets crashes.)

They write that the usual assumption of the "gap modulation method" is that the delta dithering amplitude is constant because the modulating frequency is beyond the controller bandwidth. ("gap modulation method" == established method of feedback dithering for LBH image generation)
They write that this assumption does not always hold. Especially for fast-scanning high-bandwidth scanners.
And I take (my interpretation reading between lines) they mean the problem was not solved till now because this problem was overlooked.

All this was done with big slow macroscopic piezo based STMs.
(An in house own design STM of Zyvex and an omicron STM for comparison.)

So we are left to wonder how much this will do for fast and lightweight MEMS based STMs.

Next up, to widen the data bottleneck, this needs to be electrically parallelized and combined with (nontrivial) nanomechanical demultiplexing.
All that while reducing self assembly failure rate and further extending and improving improving (the already demonstrated) convergent/hierarchical self assembly capabilities.

The emergence of unconventional biomineralization research is also a milestone I'm eagerly waiting for.
(Unconventional in the sense of not trying to recreate strong (but non AP) composite materials like mica but trying to create less strong but more versatile pure and AP single crystals of desired shape.)

The last nanotech conference I went to was almost a decade ago so I feel a bit out of touch with developments, but the two really promising fronts at that time seemed to be Chris Schafmeister's "molecular Lego" building blocks, which were small rigid molecules with (iirc) a pretty standardized set of bonding interfaces with one another, and Paul Rothemund's work on DNA origami, which has been recently used in cancer treatment. DNA origami has led to some interesting developments, but after ten years I'm a little surprised that neither of these fronts has yielded more dramatic advances than we see around us today.

Back in the old days we used to hear complaints that software wasn't advancing quickly enough. These days there seems to be plenty of progress in software, although most of it seems narrowly focused on either web applications or the internet of things.

So just being curious, was I over-optimistic in my assessment of the work of Schafmeister and Rothemund, or are we lagging in design software? And is Burke's work as revolutionary as some of the hype is making it out to be? When am I finally going to get my respirocytes and utility fog?

An image out of this paper made it into Wikipedia.
I think it's the first CC licensed image of 3D wiremesh DNA stuff on Wikipedia:commons.wikimedia.org/wiki/File:DNA_origami_rotaxanes.jpg
Assuming the uploader "Materialscientist" was one of the creators (unlikely - comment to high res upload says "from PDF")
or had permission from the creators or the upload is tolerated which is not clear from what I find.
I'd love to use that image but as long as I'm not clear about the license I rather not.

On the microfluidics front there's a new website for open source R&D collaboration (created by MIT Media Lab).metafluidics.org/
I see how this could notably accelerate progress if adopted by the subset of struct-DNA-nanotec (& other foldamer) researchers/developers.]]>…]]>Wed, 14 Sep 2016 17:09:39 +0000
This stands for Inter Nodal Connector Architecture.

You can see some of the basic designs and diamondoid-inspired structures made with this.

The idea is to take carbon wires such as fullerene nanotubes and make these systems:

Series of interlocking nodes, tubes, springs, that can be used to build super strong and flexible as well as lightweight structures.
Electrical, Optical, and other systems can be coupled to the mechanical systems to make smart, shape-changing active materials.

All feedback on this is welcomed.

One of the big plusses with the INCA system as the bootstrap for MNT is this: It is based on the curvature we see in the biological and natural world. Look at the spirals and curved structures in nature, such as in DNA helixes and protein chains and more.]]>Fri, 27 Mar 2015 16:33:30 +0000http://www.foresight.org/GrandPrize.1.html ?

It is difficult to tell if any progress has been made toward making such devices possible. The only technology I am aware of (I have not done a good job of keeping track of these things the past few years) that I think may be the shortest route is use of wet nanotech and genome engineering to either build tools that then build the devices or that can build the devices directly.
]]>Fri, 27 Mar 2015 14:31:05 +0000
If the position of one magnet interfered mechanically with the motion of another magnet, then you could build rod-logic, and decode a series of external field manipulations into arbitrary patterns of actuation.

Small particles for computation, larger particles for actuation (force should scale as cube of length).

Of course, rod-logic can directly sense physical/mechanical state, including some kinds of molecule binding.